The use of hematoporphyrin and its acetylated derivative mixture hematoporphyrin derivative (HPD) systemically, combined with irradiation, for the detection and treatment of malignant cells has, by this time, some considerable history. HPD is a mixture of porphyrins including hematoporphyrin itself, hydroxyethyl vinyl deuteroporphyrin, protoporphyrin, and dihematoporphyrin ethers. (See, e.g., "Porphyrin Photosensitization", Kessee, D., et al, eds. (1983) Plenum Press.)
HPD seems "naturally" capable of localizing in malignant cells. When irradiated, it has two properties which make it useful. First, when irradiated with ultraviolet or visible light, it is capable of fluorescence, and thus is useful in diagnostic methods related to detection of malignancy (see, for example, Kessee, et al (supra); Gregory, H.B. Jr., et al, Ann Surg (1968) 167:827-829). More pertinent to the present invention is the capacity of HPD, when irradiated with visible light, to exhibit a cytotoxic effect on the cells in which it is localized (see, for example, Diamond, I., et al, Lancet (1972) 2:1175-1177; Dougherty, T. J., et al, Cancer Research (1978) 38:2628-2635; Dougherty, T. J., et al, "The Science of Photo Medicine" (1982) J. D. Regan & J. A. Parrish eds., pp. 625-638; Dougherty, T. J., et al, "Cancer: Principles and Practice of Oncology" (1982) V.T. DeVita Jr., et al, eds., pp. 1836-1844). Although it has not been definitively established, the effect of HPD in killing cells seems to be due to the formation of singlet oxygen upon irradiation (Weishaupt, K.R., et al, Cancer Research (1976) 36:2326-2329). Several mechanisms for this effect have been proposed, and it has recently been shown that the active ingredient in HPD which mediates the cytotoxic effect of visible light irradiation is the mixture of dihematoporphyrin ethers (DHE) (Dougherty, T.J., et al, "Porphyrin Localization and Treatment of Tumors" (1984) pp. 301-314; Dougherty, T. J., CRC Critical Reviews in Oncoloqy/Hematology (1984) 2:83-116).
A purified form of the active component(s) of HPD is obtained by adjustment of pH to cause aggregation and recovery of the aggregate, as disclosed in U.S. Pat. No. 4,649,151. The purified form, called DHE in the patent, is marketed under the trademark Photofrin.RTM. II and has been used in a manner completely analogous to HPD.
While the treatment of tumors with HPD relies on the intrinsic ability of HPD to localize in malignant cells, a considerable improvement and refinement in specificity has been achieved by conjugating the hematoporphyrin to tumor-specific antibodies. For example, when hematoporphyrin was coupled to monoclonal antibodies directed to a murine myosarcoma cell line Ml, administration of anti-Ml hematoporphyrin-conjugates to tumor-bearing animals followed by exposure to incandescent light resulted in the suppression of Ml growth (Mew, D., et al, J Immunol (1983) 130:1473-1477). In additional work, hematoporphyrin was conjugated to a monoclonal antibody specific to an antigen associated with a human leukemia (CAMAL) and the conjugates were shown to mediate the irradiation-induced killing of leukemic cells specifically, in vitro (Mew, D., et al, Cancer Research (1985) 45:4380-4386).
While the conjugation of hematoporphyrin to immunoglobulins specific for targeted cells refines the ability of the hematoporphyrin to home to the desired cells or tissue, this still does not solve another problem ancillary to this general therapeutic approach, namely that the wavelength for irradiation required to activate the hematoporphyrin or HPD, which is in the range of 630 nanometers, is also an energy which is readily absorbed by the porphyrins and other natural chromophores in the blood and other tissues. Therefore, relatively large amounts of the hematoporphyrin or HPD must be administered, often resulting in oversensitization of the patient to light in general. It would be desirable to administer compounds to mediate the effects of irradiation in a lower amount, thus avoiding the problems of hypersensitivity exhibited nonspecifically throughout the subject organism. The activity of certain of these compounds was described in a paper by Richter, A.M., et al, in J Natl Cancer Inst (1987) 79:6, mailed to subscribers on 19 Jan. 1988. The invention is directed to the use of such compounds.